Pickling process



UNITED STATES PATENT OFFICE.

JOHN COULSON, OF W'ILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY, A CORPORATION OFPENNSYLVANIA. I

PICKLING PROCESS.

No Drawing.

To all whom it may concern:

. resident of Wilkinsburg, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Pickling Processes, of which the following is a specificatiom My invention relates to the cleansing of metallic objects by electrolytic means, and it has for one of its objects to provide a process of the character indicated, whereby objects of iron, steel and other metals may be effectively cleansed without impairing their strength, resiliency or other physical properties.

Another object of my invention is to provide an electrolytic pickling process by which the surface cleansing of objects of iron or other magnetic .material may be combined with an artificial magnetic aging of the material which will tend to prevent further change in the magnetic permeability of such objects.

The pickling of iron and steel for the purpose of removing the surface scale has heretofore been performed, either by simple immersion of the objects in acid, usually sulfuric acid, or by making the objectto be pickled an electrode of an electrolytic cell havin a sulfuric acid electrolyte. It has been ound that iron and steel springs and other objects which must necessarily have a high degree of resiliency cannot be satisfactorily ickled by the use of. acid alone or as'the cat ode in an acid electrolyte but become exceedin ly brittle on account of the occlusion or a sorption by the metal of the hydrogen evolved in the nascent state upon the surface of'the metal in both of these processes. It seems probable that the hydrogen forms an alloy with the metal. It has also been found that the method of pickling in which the object being treated is made the anode of an electrolytic cell is unsatisfactory for the reason that a considerable portion of the material of the anode is removed in the process. For this reason, such iron and steel objects as are injured b an increase in their brittleness or by'pitting of their surface are commonly cleansed by sand blasting, instead of by pickling, although the sand blasting treatment is much more expensive and inconvenient.

. I have discovered that the'efiect of brit Specification of Letters Patent.

Patented Apr. 12, 1921.

Application filed October a, 1917. Serial No. 195,335.

tleness of metal treated as a cathode in the ickhng process may be overcome by subjectmg the treated object to a subsequent treatment as an anode. This removes the hydrogen and restores the elasticity of the material. small amount of the iron may be dissolved 1f the treatment during the final step be too long continued, but, in case of springs and other resilient objects, such trifling loss of 1ron is negligible in view of the substantial gain in strength and permanent magnetic quality effected by my process.

The sulfuric acid electrolyte-used in carrying out my process should be concentrated, acid having a specific gravity of about 1.20 being suitable for this purpose. The object to be treated is made one electrode and the other electrode, which is preferably of lead, may be; the acid-containing tank ltself, although this is not essential. The electrodes are preferably connected to the source of electrical energy by a circuit including a reversing switch which is first thrown. in such direction that the object being treated is made the cathode and, after the oxid has been removed, is thrown to reverse position to make the treated object the anode. The current density at the anode in the final step of the treatment may suitably be about amperes per square foot.

The time requiredfor picklin w1ll vary in substantial eflect upon its magnetic permeability. This appears to result from the liberation of nascent oxygen from the surface of the metal and to a gradually decreasing extent within .the pores of the metal, such oxygen combining with the occluded hydrogen which results from the step of removlng'the oxid, as well as with the occluded oxygen always present in wrought iron and steel.

It is to be understood that the specific materials, proportions and conditions mentioned above are intended to be merely illus trative and not as imposing limitations upon my invention which is defined by the scope of the appended claims.

I claim as my invention:

1. The process that comprises subjectingv a ferrous metal, as an electrode of one polarity and subsequently -as an electrode of opposite polarity to the action of an electric current in the presence of an electrolyte containing sulfurlc acid.

2. The process that comprises subjecting a ferrous metal as a cathode and subsequently as an anode to the action of an electric current in the presence of an acid electrolyte.

3. The process of pickling metal that comprises removing the surface scale from the metal and subsequently subjecting the metal, as an anode, to the action ofan electric current 1n the presenceof an electrolyte containing an oxygen acid.

4:. The process of pickling metal that comprises electrolytically removing surface oxid from the metal and subsequently sub jecting the metal, as an anode, to the action of an electric current'in the presence of, an acid electrolyte.

5. The process of removing occluded hydrogen from metal that comprises subject- "ing the metal, as an anode, to the action of an electric current in the presence of an electrolyte containing concentrated sulfuric acid.

and other metallic objects requiring high resiliency that comprises subjecting the object, as an anode, to the action of an electric current in the presence of an electrolyte, to

remove occluded hydrogen from said object.

7. The process that comprises immersing a metal object in an electrolyte containing concentrated sulfuric acid and passing an 6. The process of treating steel springs electric current of a density of about TJOHN OOULSON. 

